An external force applied to a person with the purpose of walking aid is preferably controlled to an appropriate one in relation to an internal force that arises due to his or her will according to the progress of rehabilitation exercise or the like. Therefore, it is conceivable to measure a joint torque on the basis of a myoelectric signal that occurs in a human body and to apply a torque (external force) of an appropriate level according to the joint torque to the person.
Conventionally, there has been suggested a technology of estimating a muscle force of a leg by an output from a pressure sensor or the like attached to the toe or heel of a sole and applying a support force to the leg through the device attached to the leg for reducing a load on muscles of the leg if the muscle force is greater than a reference value (for example, refer to paragraphs 0006 to 0012 and FIGS. 1 to 4 of Japanese Patent Laid-Open No. 2004-105261). Moreover, there has been suggested a technology of measuring a myoelectric signal that occurs in a human body and measuring a joint torque or the like of the animal concerned based on the myoelectric signal (for example, refer to paragraphs 0038 to 0062 of Japanese Patent Laid-Open No. 2001-286451).
If there is any change in muscle fatigue degree or in the contact condition between electrodes and the body due to perspiration or the like, it is projected that the relation between the myoelectric signal and the joint torque changes even in the same person and that simply adopting the conventional technologies does not provide a desired force applied to the person based on the myoelectric signal.
Therefore, the object of the present invention is to provide a method and system capable of controlling an external force applied to an animal in such a way as to achieve as a target relation the relation between the external force and a motion variable varying with the motion of the animal and a program for providing a computer with the control functions.